HMF is an important compound with many industrial applications such as use in polymers, solvents, surfactants, pharmaceuticals, and plant protection agents. However, the oxidation derivatives of HMF also have important commercial value. For example, 2,5 diformylfuran (DFF) has various useful applications such as a monomer; as a starting material for the synthesis of drugs, antifungal agents, nematocides and ligands; in photography; and as a cross-linking agent for polyvinyl alcohol. 2,5 furandicarboxylic acid a.k.a. furandiacid (FDCA a.k.a FDA) represents one key intermediate substance and is a suitable starting source for the formation of various furan monomers required for the preparation of non-petroleum-derived polymeric materials.
Many methods have been proposed for making DFF and FDCA. However, these reactions provide low yields, poor selectivity and are not environmentally friendly. For example, it is known that the synthesis of DFF from fructose can be done in a two step process, namely, by dehydration of fructose in a high boiling solvent such as dimethylsulfoxide (DMSO) to form HMF, followed by in situ catalytic air oxidation also in the presence of DMSO to form a mixture of DFF, FDCA and various other reaction side products.
Also, it has been shown that DFF or FDCA could be made from HMF by oxidation in the presence of dissolved oxygen at about 1000 psi, and a catalyst system containing Co(II), Mn(II), and a Br salt preferentially also including Zi (W. Partenhemier & V Grushin: Adv. Synth. Catal. (2001) 343, 102-111). However the selectivity for DFF was at most 69% in a catalyst system of Co/Mn/Br, and at most 73%. in a catalyst system of Co/Mn/Br/Zr. The best selectivity for FDCA was 73% in a catalyst system of Co/Mn/Br/Zr and at most about 35% with the same catalyst system but without the Zr. The ability to convert HMF into one predominant oxidation product is difficult due to the reactivity of the aldehyde and alcohol moieties of the HMF molecule. In the above mentioned reference, selectivity between DFF and FDCA as the predominant product was affected by using lower reaction temperatures (50-75° C.) for making DFF, and higher reaction temperatures for making FDCA (typically 100-125° C.).
FDCA is a difficult product to handle. It tends to precipitate in solvents used for oxidation when the temperature is raised and tends to co-precipitate with side products. It would be beneficial if an FDCA precursor could be made that is easy to separate and which could subsequently be converted to FDCA in a different reaction. Also it would be beneficial to find other routes to selective preparation of DFF versus FDCA by oxidative methods. The present invention provides for these and other needs that will be apparent from the description that follows.